Optical disk apparatus using tilt and aberration correction control system

ABSTRACT

A tilt control apparatus includes an orthogonal shift detector ( 9 ) which detects an orthogonal shift by comparing a pair of a plurality of tap coefficients (C 1 , . . . , C 7 ) of a FIR filter and generates an orthogonal shift signal, and an actuator varies the inclination of the optical axis of the light beam to correct the orthogonal shift, and a tilt controller ( 10 ) controls the drive of the actuator in accordance with the orhogonal shift signal to minimize the orthogonal shift. In the information recording operation, the orthogonal shift obtained based on a recording track is previously stored in a temporary storage portion and the stored orthogonal shift is used to conduct the tilt control.

This application is a divisional application of Ser. No. 10/407,213,filed Apr. 7, 2003 now abandoned, which is a divisional application ofSer. No. 09/537,869, filed Mar. 29, 2000 now U.S. Pat. No. 6,577,568.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an optical disk apparatus forrecording and/or reproducing information to and/or from an optical disk,and in particular to an optical disk apparatus having an aberration ortilt correction control system for maintaining an orthogonalrelationship between an optical axis of a light beam projected by anoptical pickup device and an information recording surface of theoptical disk.

2. Description of the Prior Art

High speed random access is possible with disc-shaped recording medium,and a high recording density can be achieved by formatting a disk with anarrow data track pitch and pit pitch.

Optical disks such as a DVD, which is typical, have been widely used inrecent years as a large capacity recording medium because of a highrecording density. Further advances in recording density have also beenachieved to further increase storage capacity. Optical disks, however,are typically made from low rigidity materials such as polycarbonate,and even disk deflection or deformation due to warp or bending caused bythe dead weight of the disk per se cannot be ignored.

In the case where original data recorded on, for example, an opticaldisk medium is reproduced by means of an optical pickup device, if anoptical axis of an object lens of the pickup device is not perpendicularto the surface of the disk but inclined at some angle with respect tothe orthogonal relationship to the surface of the disk, the beam spotprojected onto the disk surface is distorted due to the aberrationthereof, and there may undesirably cause a distortion in a waveform ofthe reproduced signal output of the optical pickup device. It is notedhere that the inclination error with respect to the orthogonalrelationship is referred to as “orthogonal shift” or “tilt”,hereinafter.

Moreover, due to the aberration distortion caused in the beam spot, thereflection light beams reflected from adjacent recording pits formed onthe disk undesirably interfere with each other. Thus, the modulationdegree of the reproduction signal is deteriorated, and there may becaused a shift error in a peak time (referred to as “peak shift”hereinafter) of the reproduction signal, resulting in occurrence of adiscrimination error of the information reproduction (RF) signal to be aproblem.

As a method of removing distortion components included in thereproduction signal waveform, there has been conventionally used anadaptive equalizer utilizing a finite impulse response filter (referredto as “FIR filter”, hereinafter). In this method, an adaptiveequalization is recently carried out in a digital data processing systemby previously quantizing the reproduced signal using an A/D converter.

Particularly in recent years, however, the data recording density on therecording medium has been remarkably increased and distortion of thereproduction signal due to inter-code interference of the recorded dataon the medium is increased, and also a noise influence in a datatransmission path can not be ignored because of reduction in amplitudeof the reproduction signal. Also, the reproduction signal is sensiblydeteriorated by a slight tilt of the disk or a defocus condition in theplayback system.

Specifically, in the case of using an optical disk such as DVD-RAM forcompatibly recording and reproducing information, such a tilt anddefocus condition badly affect both the recording and reproducingoperations. Therefore, the aberration correction must be performed witha further higher accuracy. In this situation, as a method of removingthe aberration distortion components included in the reproduction signalwaveform, a tilt control or aberration correction control method iseffective for maintaining an orthogonal relationship between the opticaldisk surface and the optical axis of the optical pickup device.

A conventional tilt control apparatus is suggested, for example, in theJapanese Laid-Open Patent Publication No. Tokkai-Sho 61-51630, whichdiscloses that the tilt control apparatus detects an error in theorthogonal relationship between a disk surface and an optical axis of alight beam irradiated onto the disk by using tilt photo-sensors, therebymaintaining the orthogonal relationship based on the orthogonal errorsignal detected by the photo-sensors.

However, this conventional tilt control apparatus has followingproblems. Specifically, since a pair of photo-sensors are disposed onthe right and left sides of the object lens of the optical pickupdevice, and the apparatus is made large in size and complicated inconstruction. Moreover, if the characteristics of the photo-sensors arevaried in time lapse, an offset is generated to cause an error in theorthogonal relationship. Therefore, a normal orthogonal relationshipcannot be maintained even if the orthogonal error is set to zero. Also,a tilt control cannot be performed in a circumferential direction (i.e.,track tangential direction) of the disk.

In order to solve these problems, another conventional tilt controlsystem is suggested, for example, in the Japanese Laid-Open PatentPublication No. Tokkai-Hei 5-174406, which discloses that the orthogonalshit error in the circumferential (track tangential) direction includedin the reproduction signal is detected and corrected based on the shiftin the peak time (i.e., peak shift) of the reproduction signal duringthe operation of reproducing the information from the disk in a pulsephase modulation (PPM) system.

However, in recent optical disk apparatuses, the information is mainlyrecorded on the disk in a pulse width modulation (PWM) system in orderto obtain a higher recording density. Therefore, there has been aproblem that the above conventional tilt control system adapted to thePPM recording system can not be utilized in the data reproduction systemadapted to the PWM recording system. Moreover, there has been a problemthat a tilt correction control in the circumferential (.e., tracktangential) direction of the disk can not be performed during the datarecording operation.

SUMMARY OF THE INVENTION

The present invention has been developed to solve these problems and hasan object to provide an aberration correction control apparatus or tiltcontrol apparatus, which can be utilized in the data reproduction systemadapted to the PWM recording system, and also the tilt correctioncontrol in the circumferential (.e., track tangential) direction of thedisk can be performed during the data recording operation as well asduring the data reproducing operation.

Another object of the present invention is to provide an optical diskapparatus using the improvement of the aberration correction controlapparatus or tilt control apparatus.

In order to achieve the objects mentioned above, a first aspect of thepresent invention provides a tilt control apparatus for controlling tominimize an error of an orthogonal shift in an orthogonal relationshipbetween an optical disk surface and an optical axis of a light beamirradiated from an optical pickup onto the optical disk in combinationwith an adaptive equalizer adaptively renewing a plurality of tapcoefficients of a FIR filter in an optical disk apparatus. The tiltcontrol apparatus comprisses: an orthogonal shift detector for detectingthe orthogonal shift of the light beam using the tap coefficients of theadaptive equalizer and generating an orthogonal shift signal inaccordance with the detected orthogonal shift; an inclination drive unitfor varying the inclination of the optical axis of the light beam tocorrect the orthogonal shift; and a drive control unit for controllingthe inclination drive of the inclination drive unit in accordance withthe orhogonal shift signal to minimize the orthogonal shift of the lightbeam.

The orthogonal shift detector detects the orthogonal shift by comparingat least one pair of the tap coefficients symmetrical with respect to acenter position in time delay order thereof.

The number of the plurality of the tap coefficients is odd in time delayorder, and the drive control unit controls the inclination drive of theinclination drive unit in a manner that at least a pair of thesymmetrical tap coefficients are substantially made coincident with eachother.

A second aspect of the present invetion provides an optical diskapparatus for recording and reproducing information to and from anoptical disk, which comprises: an optical pickup irradiating a lightbeam onto an optical disk surface for recording and reproducing theinformation to generate an analogue reproduction signal therefrom; anA/D converter for converting the analogue reproduction signal into adigital form; an adaptive equalizer receiving the digital reproductionsignal from the A/D converter and adaptively renewing a plurality of tapcoefficients of a FIR filter; and a tilt control apparatus forcontrolling to minimize an error of an orthogonal shift in an orthogonalrelationship between an optical disk surface and an optical axis of alight beam irradiated from the optical pickup onto the optical disk,

wherein the tilt control apparatus comprises: an orthogonal shiftdetector for detecting the orthogonal shift of the light beam using thetap coefficients of the adaptive equalizer and generating an orthogonalshift signal in accordance with the detected orthogonal shift; aninclination drive unit for varying the inclination of the optical axisof the light beam to correct the orthogonal shift; and a drive controlunit for controlling the inclination drive of the inclination drive unitin accordance with the orhogonal shift signal to minimize the orthogonalshift of the light beam.

Thus, in the information recording operation, the orthogonal shiftobtained based on a recording track is previously stored in a temporarystorage portion and the stored orthogonal shift is used to conduct thetilt control. Thus, the tilt control apparatus can be utilized in thedata reproduction system adapted to the PWM recording system, and alsothe tilt control in the circumferential direction of the disk can beperformed during the data recording operation as well as during the datareproducing operation.

A third aspect of the present invention provides an aberration controlapparatus for controlling to minimize an aberration contained in a spotof a light beam irradiated from an optical pickup onto the optical diskin combination with an adaptive equalizer adaptively renewing aplurality of tap coefficients of a FIR filter in an optical diskapparatus. The aberration correction control apparatus comprises: anaberration detector for detecting the aberration of the light beam spotusing the tap coefficients of the adaptive equalizer and generating anaberration detection signal in accordance with the detected aberration;an aberration correcting unit for correcting the aberration of the lightbeam spot; and a correction control unit for controlling the aberrationcorrection of the aberration correcting unit in accordance with theaberration detection signal to minimize the aberration of the light beamspot.

The aberration detector detects the aberration by comparing at least onepair of the tap coefficients symmetrical with respect to a centerposition in time delay order thereof.

The number of the plurality of the tap coefficients is odd in time delayorder, and the correction control unit controls the the aberrationcorrection of the aberration correcting unit in a manner that at least apair of the symmetrical tap coefficients are substantially madecoincident with each other.

The aberration correcting unit is segmented into a plurality of liquidcrystal tilt correction elements, each of the liquid crystal elementshaving an independently variable light refractive index, and theaberration correction control is executed by varying the lightrefractive indexes of the liquid crystal elements individually.

A fourth aspect of the present invention provides an optical diskapparatus for recording and reproducing information to and from anoptical disk, which comprises: an optical pickup irradiating a lightbeam onto an optical disk surface for recording and reproducing theinformation to generate an analogue reproduction signal therefrom; anA/D converter for converting the analogue reproduction signal into adigital form; an adaptive equalizer receiving the digital reproductionsignal from the A/D converter and adaptively renewing a plurality of tapcoefficients of a FIR filter; and an aberration control apparatus forcontrolling to minimize an aberration contained in a spot of a lightbeam irradiated from the optical pickup onto the optical disk,

wherein the aberration control apparatus comprises: an aberrationdetector for detecting the aberration of the light beam spot using thetap coefficients of the adaptive equalizer and generating an aberrationdetection signal in accordance with the detected aberration; anaberration correcting unit for correcting the aberration of the lightbeam spot; and a correction control unit for controlling the aberrationcorrection of the aberration correcting unit in accordance with theaberration detection signal to minimize the aberration of the light beamspot.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bereadily understood from the following detailed description taken inconjunction with preferred embodiments thereof with reference to theaccompanying drawings, in which like parts are designated by likereference numerals and in which:.

FIG. 1 is a block diagram of an optical disk apparatus according to afirst embodiment of the present invention;

FIG. 2 is a schematic plan view showing a construction of an opticalpickup device according to the first embodiment;

FIG. 3 is a conceptual block diagram showing a construction of anadaptive equalizer;

FIG. 4 is a block diagram showing a construction of a FIR equalizingfilter;

FIG. 5 is a block diagram showing a construction of an equalizing errordetection unit;

FIG. 6 is a block diagram showing an essential construction of a LMScoefficient calculation unit;

FIG. 7 is a graph view showing a learning result of the LMS coefficientcalculation unit;

FIG. 8 is a graph view shown an essential part of the learning resultshown in FIG. 7;

FIGS. 9A, 9B and 9C are schematic views explaining a tilt adjustingdirection;

FIG. 10 is a block diagram of an optical disk apparatus according to asecond embodiment of the present invention;

FIG. 11 is a schematic plan view showing a construction of an opticalpickup device according to the second embodiment;

FIG. 12 is a schematic plan view showing a liquid crystal aberrationcorrection element adapted to the optical pickup device shown in FIG.11;

FIG. 13 is a schematic plan view showing another example of a liquidcrystal aberration correction element;

FIG. 14 is a block diagram of an optical disk apparatus according to athird embodiment of the present invention;

FIGS. 15A, 15B, 15C, 15D, 15E, 15F and 15G are timing charts forexplaining operations of the third to sixth embodiments;

FIG. 16 is a block diagram of an optical disk apparatus according to afourth embodiment of the present invention;

FIG. 17 is a block diagram of an optical disk apparatus according to afifth embodiment of the present invention;

FIG. 18 is a block diagram of an optical disk apparatus according to asixth embodiment of the present invention; and

FIG. 19 is a block diagram for explaining a data recording andreproducing operation of an optical disk apparatus according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description proceeds, it is to be noted that, since the basicstructures of the preferred embodiments are in common, like parts aredesignated by the same reference numerals throughout the accompanyingdrawings.

Firstly, the following briefly describes an example of a configurationand concept of a recording and reproducing operation of an optical diskapparatus according to the present invention with reference to FIG. 19.

As shown in FIG. 19, the optical disk apparatus includes an optical disk1, disc motor, optical pickup device 2, laser drive circuit (LPC),modulator/demodulator, error detector and corrector (ECC), interfaceunit, amplifier/adaptive equalizer/digitizer, focus tracking controller,and control CPU 15. The disc motor rotates the optical disk 1, and theoptical pickup device 2 comprises an optical lens, actuator andsemiconductor laser to thereby read and write data to and from theoptical disk. The laser drive circuit (LPC) drives the laser of theoptical pickup device 2.

During the recording operation, the modulator/demodulator digitallymodulates the data to a form suitable for recording, and demodulates thedata during the reproduction operation. The error detector and corrector(ECC) executes error detection and correction. The interface unit (I/F)controls interfacing with a host computer through an external input andoutput terminals. The amplifier/adaptive equalizer/digitizer amplifiesthe reproduction signal and adaptively equalizes the amplified data anddigitizes the resultant amplified reproduction signal. The focustracking controller tracks the optical pickup device to a target track,and focuses the laser beams on the recording surface of the opticaldisk.

The control CPU is a controller providing overall control of the opticaldisk apparatus, that is, executing target address extraction fordetermining a target sector address for reading or writing, reproductioncontrol, adaptive equalizing control, tilt aberration control, commandcontrol such operations as command analysis, recording control, and thelike. The control CPU is preferably a microprocessor whereby thefunctions of the component units thereof can be accomplished insoftware.

The data recording operation by the optical disk apparatus thusconstructed is described briefly below.

User data sent from a host computer via the external terminal isinputted via the interface unit (I/F) and error detector and corrector(ECC) and is supplied to the modulator/demodulator. Themodulator/demodulator digitally modulates the error correction codeddata. In the meanwhile, the control CPU designates a target track to thefocus tracking controller. The focus tracking controller moves theoptical pickup device to the target track to record the input user data.The digitally modulated modulation data is sent to the laser drivecircuit (LPC), which modulates the laser power according to themodulation data, and records the data to the data recording area of thetarget sector on the optical disk.

The operation for reproducing data is described briefly next. When datais reproduced, the control CPU sends the target track for datareproduction to the focus tracking controller, and the focus trackingcontroller tracks the light beam from the optical pickup device to thetarget track. In the same manner as in the recording operation, adigital read signal is generated from the light beam reflected from theoptical disc via the amplifier/adaptive equalizer/digitizer, and thetarget sector is detected by the modulator/demodulator. Themodulator/demodulator digitally demodulates the digital read signalobtained from the data recording area of the target sector, and suppliesthe result as the reproduced data to the host computer via the errordetector and corrector (ECC) and passed through the interface unit(I/F).

The above operations are Controlled by the control CPU and executed as asingle continuous operation. It should be noted that description of atiming control circuit and other components common to a conventionalrecording and reproducing apparatus for an optical disk recording mediumis omitted here.

First Embodiment

FIG. 1 shows a block construction of a data reproducing apparatus of anoptical disk apparatus including a sampled amplitude read channelaccording to a first embodiment of the present invention where the readchannel reads a reproduction signal from a disk medium and generatesbinary data therefrom, including an adaptive equalizer in a digital datareproducing apparatus. In this construction, an optical disk 1 is usedas an example of a disk medium which has a sector format of aperiodically wobbling recording groove. An optical pickup device 2applies laser beams to the optical disk and reads the recorded databased on the quantity of the reflected light beams and generates anelectric signal therefrom. A preamplifier 3 amplifies the output signalof the pickup is device and generates a reproduction RF signal.

The read channel of the data reproducing apparatus includes an auto-gaincontroller (AGC) 4 for adjusting an amplitude of the reproduction signalto have a constant amplitude, an equalizer 5 for improving frequencycharacteristics of the output signal of the AGC 4, an A/D converter 6for sampling the reproduction signal with a channel clock signal toconstitute a digital read channel, and a PLL circuit 7 for phase-controlwith the output signal of the A/D converter 6 to generate asynchronization clock synchronized with the digital signal.

The data reproducing apparatus further includes a digital adaptiveequalizer 8 for adaptively equalizing the discrete sampled data outputof the A/D converter 6 to execute a predetermined partial response (PR)equalization, a Viterbi decoder 11 for generating a most likelihoodbinary data from the equalization results of the discrete sampled dataof the reproduction signal, and a demodulator 12 for demodulating thebinary digitized data output of the Viterbi decoder 11.

The data reproducing apparatus further includes an orthogonal shiftdetector 9 which receives tap coefficients of a FIR filter portion ofthe adaptive equalizer 8 and detects an orthogonal shift (i.e., tilt)between the recording surface of the optical disk 1 and the optical axisof the light beam irradiated from the optical pickup device 2 based onthe tap coefficients to thereby generate an orthogonal shift signalcorresponding to the orthogonal shift amount. The data reproducingapparatus further includes a tilt controller 10 for control-driving atilt actuator of the optical pickup device 2 in accordance with theorthogonal shift signal output of the orthogonal shift detector 9 toadjust the tilt actuator to maintain the orthogonal relationship betweenthe optical disk surface and the optical axis of the light beams.

FIG. 2 shows a construction of the pickup device 2 having the tiltactuator as mentioned above. The optical pickup device 2 includes anobject lens 2 a for condensing light beams, a holding member 2 b forholding the object lens 2 a, first and second magnetos 2 c and 2 ddisposed on the end portions of the holding member 2 b in the diskcircumferential (i.e., track tangential) direction, a securing wire 2 efor substantially securing the holding member 2 b to a substrate of theoptical pickup device, and first and second electromagnetic coils 2 fand 2 g which are opposed to the first and second magnetos 2 c and 2 d,respectively, with a prescribed space therefrom. In this construction,the direction and quantity of the current flowing through theelectromagnetic coils 2 f and 2 g are controlled so that the inclinationof the object lens 2 a can be adjusted in the track tangential directionof the disk.

In this construction, the first and second magnetos 2 c and 2 d and thefirst and second electromagnetic coils 2 f and 2 g constitute the tiltactuator which functions as an orthogonal shift correction drive means.In this arrangement, it is noted here that the tilt actuator may adjustthe inclination drive of the entire part of the optical pickup device inthe track tangential direction of the optical disk.

FIG. 3 shows a construction example of the adaptive equalizer 8 shown inFIG. 1, which includes a FIR filter portion 21, an equalization errordetector portion 22 and a tap coefficient renewer portion 23. The tapcoefficient renewer portion 23 recursively renews the coefficients ofthe FIR filter portion 21 in accordance with the following Equation (1).The renewed tap coefficients are fed back to the FIR filter portion 21and also fed to the orthogonal shift detector 9 in common.

Adaptive equalization is carried out in a digital data processing systemby previously quantizing the reproduced signal using an A/D converter.The adaptive equalizer 8 operates according to a well known least meansquare (LMS) algorithm.

According to the least mean square (LMS) algorithm, the FIR filtercoefficient vector of the adaptive equalizer is recursively renewedbased on Equation (1) as below:h(n+1)=h(n)+μ·e(n)·u(n)  (1)where h(n) represents a vector of filter coefficients beforeequalization; h(n+1) represents a vector of filter coefficients afterequalization; μ is a programmable gain; e(n) represents a sample errorbetween the filter's actual output and a desired output; and u(n)represents a vector of sample values input to the FIR filter. By thisarrangement, the filter tap coefficients (i.e., frequency and phaseresponse of the filter) are adapted until a minimum sample error isachieved.

FIG. 4 shows a construction example of the FIR filter portion 21 whichreceives the digital sampled data of the reproduction signal from theA/D converter 6. The FIR filter portion 21 includes delay units 30 fordelaying the input sampled data in turn every reproduction clock periodsobtained by the PLL 7, multipliers 31 a to 31 g (represented by “31”hereinafter) for multiplying coefficients Ci (i=1, . . . , 7) appliedfrom the tap coefficient renewer portion 23 by the delayed values Si(i=1, . . . , 7) input to or output of the delay units 30, an adder 32for obtaining a total sum Y(t)=ΣCi(t)×Si(t), where i indicates aninteger from 1 to 7 and t indicates a present time, and further includesa signal selector 33 for selecting the input or output signal of eachdelay unit 30 in accordance with a counted value of a coefficientselecting counter (not shown) for time division processing. By thisarrangement, the delayed values Si(t) output of the delay units 30 arefed to the equalization error detector 22 via the signal selector 33while the total sum Y(t) output of the adder 32 is also fed to the errordetector 22 and is also generated as the equalization result to beapplied to the Viterbi decoder 11.

FIG. 5 shows a construction example of the equalization error detector22 which includes a temporary judger portion 41 receiving the total sumY(t) output of the adder 32 and judging an equalization target value TLthereof, a target register 42 for registering the equalization targetvalue TL, a subtracter 43 for subtracting the total sum Y(t) output ofthe adder 32 from the equalization target value TL output of the targetregister 42, a first multiplier 44 for multiplying the subtractionresult output of the subtracter 43 by the selected delayed signal outputof the signal selector 33, and a second multiplier 45 for multiplyingthe output of the first multiplier 44 by the predetermined programmablegain factor μ.

FIG. 6 shows a construction example of the tap coefficient renewer 23which includes a coefficient register 51 for holding an initialcoefficient value Co or renewed tap coefficients Cm, a coefficientselector 52 for selecting the output of the coefficient register 51 inaccordance with a counted value of a coefficient selection counter (notshown) to generate the present tap coefficients and an adder 53 foradding the output of the second multiplier 45 of the equalization errordetector 22 with the output of the coefficient selector 52 to therebygenerate the renewed tap coefficients. In this construction, theregistered tap coefficients Cm output of the coefficient register 51 arefed back to each of the multipliers 31 of the FIR filter 21 and alsosupplied to the orthogonal shift detector 9.

The following describes an operation of the adaptive equalizer 8.Initially, in the step of starting up the optical disk apparatus, theinitial coefficient value Co is loaded to the coefficient register 51.The tap coefficients C1 to C7 are respectively applied to themultipliers 31 a to 31 g. When the digital reproduction signal Sn (at atime n) is sequentially applied to each of the delay units 30 of the FIRfilter 21 from the A/D converter 6, the FIR filter 21 calculates thetotal sum Y(t)=ΣmSm,n×Cm,n to be outputted from the adder 32. Accordingto Equation (1) of LMS algorithm, the m-th tap coefficient Cm isobtained as below:Cm,n+1=Cm,n+μ×Sm,n(TLn−ΣmSm,n×Cm,n)  (2)where μ is a step size parameter of the programmable gain, and m denotesa tap coefficient number represented by integers 1 to 7. In the righthand of this Equation (2), ΣmSm,n×Cm,n represents the output of theadder 32, (TLn−ΣmSm,n×Cm,n) represents the output of the subtracter 43that is the equalization error, and μ×Sm,n(TLn−ΣmSm,n×Cm,n) representsthe output of the second multiplier 45. Thus, the renewed tapcoefficients Cm,n+1 are outputted from the adder 53 of the tapcoefficient renewer 23 and fed back to the coefficient register 51.

The temporary judger 41 of the equalization error detector 22 judgeswhich the target value the total sum supplied from the adder 32 of theFIR filter 21 should be equalized to, and the judgment result is appliedto the target register 42. The target register generates the judgedequalization target value TL. The subtracter 43 subtracts theΣmSm,n×Cm,n supplied from the adder 32 from the equalization targetvalue TL to generate the equalization error.

In the FIR filter 21, the signal selector 33 selects the input or outputSm of each of the delay units 30 corresponding to the m-th tapcoefficient Cm (m=1, . . . , 7) in accordance with the output of thecoefficient selection counter (not shown) and the selected signal Sm issupplied to the first multiplier 44 of the equalization error detector22. The first multiplier 44 multiplies the selected signal Sm,n atpresent time n by the equalization error obtained by the subtracter 43and the resultant value is supplied to the second multiplier 45. Thesecond multiplier 45 multiplies the output of the first multiplier 44 bythe step size parameter U and the resultant output of the secondmultiplier 45 is supplied to the adder 53 of the tap coefficient renewer23.

Similarly in the tap coefficient renewer 23, the coefficient selector 52selects the m-th tap coefficient Cm in accordance with the output of thecoefficient selection counter (not shown) and the selected tapcoefficient Cm is supplied to the adder 53. The adder 53 adds the outputof the second multiplier 45 of the equalization error detector 22 andthe present m-th tap coefficient Cm,n output of the coefficient selector52 to thereby generate a renewed m-th tap coefficient Cm,n+1. Thecoefficient register 51 newly holds the renewed tap coefficient. Theseprocesses are repeated in accordance with the coefficient counter (notshown) and the inter-code interference of the reproduction signalreproduced from the optical disk can be effectively removed to obtainthe tap coefficients C1 to C7 for forming the most preferablereproduction signal.

FIG. 7 is a graph showing equalization learning results of the tapcoefficients of the FIR filter 21 when the adaptive equalizer 8 receivesa reproduction signal actually added with a tilt in a track tangentialdirection of the disk (referred to as “T tilt” hereinafter). In thisgraph, except for the tap coefficient C4 to be applied to thecenter-positioning (i.e., fourth) multiplier 31 d, in each of thesymmetrical tap coefficients pairs (C1 and C7), (C2 and C6), and (C3 andC5) in time delay input order thereof, the tap coefficients areinterrelated to each other.

FIG. 8 is a partially enlarged graph of FIG. 7 deleting thecenter-positioning tap coefficient C4, where the horizontal axisrepresents the T tilt value and the vertical axis represents the tapcoefficient value.

FIGS. 9A, 9B and 9C show a normal condition, plus (+) condition andminus (−) condition of the tilt direction with respect to the orthogonalrelationship between the optical disk surface and the optical axis ofthe optical pickup device 2, respectively. As apparently seen from thesefigures in connection with the graph of FIG. 8, concentrating attentionto, for example, the tap coefficient pair of C1 and C7, the tapcoefficient relationship is C1<C7 when the T tilt is in the minusdirection, and the tap coefficient relationship is C1>C7 when in theplus direction. Similarly, concentrating attention to, for example, thepair of C3 and C5, the tap coefficient relationship is C3<C5 when the Ttilt is in the minus direction, and the tap coefficient relationship isC3>C5 when in the plus direction. Also, concentrating attention to, forexample, the pair of C2 and C6, the tap coefficient relationship isC2>C6 when the T tilt is in the minus direction, and the tap coefficientrelationship is C2<C6 when in the plus direction.

When the T tilt is 0 (zero), the relationships are C1=C7, C3≈C5, andC2≈C6. Accordingly, the orthogonal shift can be controlled using thecombination of the tap coefficients pairs in the orthogonal shiftdetector 9. For example, when (C7−C1) is plus, it is judged that the Ttilt is minus, and the optical pickup device 2 is adjusted to a plusdirection, and when (C7−C1) is minus, it is judged that the T tilt isplus, and the optical pickup 2 is adjusted to a minus direction, andthus the T tilt can be corrected.

For example, assuming that an ideal spot shape of the light beams to beprojected to the optical disk is true circle, when a T tilt isgenerated, the light beams are applied from the optical pickup device tothe disk surface with some inclination, and therefore the beam spotshape is elliptically distorted and there arises a biased or unbalanceddistribution in intensity of the light beams due to the effect of theaberration. The distortion of the beam spot is affected more largely inthe inclined direction of the optical pickup device. The adaptiveequalizer 8 is operated to execute the equalization in a direction toremove the effect of the aberration. Therefore, the symmetrical balancedcondition of the right and left tap coefficients in each pair withrespect to the center-positioning tap coefficient C4 is made unbalancedwhen a T tilt is caused.

That is, when the tap coefficients in each pair are made symmetrical inright and left sides, namely, when the tap coefficients in each pair arecoincident with each other, the influence of the aberration due to thetilt can be made minimum. In this connection, the relationship betweenthe unbalanced condition of the tap coefficients and the direction ofthe tilt is varied in accordance with the light beam spot and the tapinterval.

Next, the following describes a tilt control operation in thereproducing operation of the optical disk apparatus shown in FIG. 1.

The preamplifier 3 amplifies the output signal of the pickup device andgenerates the reproduction RF signal. The auto-gain controller (AGC) 4adjusts an amplitude of the reproduction signal to have a constantamplitude, and the equalizer 5 improves the frequency characteristics ofthe output signal of the AGC 4. The A/D converter 6 samples thereproduction signal with a channel clock signal to constitute a digitalread channel, and the PLL circuit 7 executes the phase-lock control withthe output signal of the A/D converter 6 to generate a synchronizationclock synchronized with the digital signal.

The digital adaptive equalizer 8 adaptively equalizes the discretesampled data output of the A/D converter 6 to execute the predeterminedequalization to generate the LMS tap coefficients C1 to C7 for formingthe most preferable reproduction signal in each of the positions in thetrack tangential direction of the disk. When the tap coefficients C1 toC7 are supplied to the orthogonal shift detector 9, the orthogonal shiftdetector 9 calculates the subtraction of, for example, (C7−C1) togenerate the orthogonal shift signal to be applied to the tiltcontroller 10.

When the orthogonal shift signal is plus, the inclination of the opticalpickup device is corrected to a plus direction as shown in FIG. 9B bycontrolling the current flowing through the first and secondelectromagnetic coils 2 f and 2 g. On the contrary, when the orthogonalshift signal is minus, the inclination of the optical pickup device iscorrected to a minus direction as shown in FIG. 9C by controlling thecurrent flowing through the first and second electromagnetic coils 2 fand 2 g. Thus, the orthogonal shift can be made minimum or substantiallyzero as shown in FIG. 9A. As a result, the T tilt of the disk can becorrected and the preferable disk reproduction signal can be obtainedwith eliminating the inter-code interference. Also, the inter-codeinterference, which can not be eliminated by the tilt control operation,is effectively processed by the adaptive equalizer 8 and the mostsuitable reproduction signal can be applied from the adaptive equalizer8 to the Viterbi decoder 11. The Viterbi decoder 11 generates a mostlikelihood binary data from the equalization results of the discretesampled data of the reproduction signal, and then the demodulator 12demodulates the binary digitized NRZI data output of the Viterbi decoder11, recovering the user data format before subjection to modulation.

As described above, according the first embodiment of the presentinvention, even in the case where an optical disk or a drive systemcomprised of an optical pickup includes a T tilt, a most suitable tiltcontrol can be executed adaptively in each position of the tracktangential direction of the disk with high accuracy by a simpleconstruction. Thus, the most suitable reproduction signal can beproduced in the disk reproducing system, and the disk reproductionmargin can be secured even with a high recording density of the disk.

Second Embodiment

FIG. 10 shows a block construction of a data reproducing apparatusaccording to a second embodiment of the present invention. The differentpoints from the first embodiment reside in the fact that, aberrrationcorrection is performed instead of performing a tilt control in thetrack tangential direction of the optical disk, using a liquid crystalaberration correction unit instead of using the tilt actuator in theoptical pickup 2, using an aberration detector 13 instead of using theorthogonal shift detector 9, and using an aberration controller 14instead of using the tilt controller 10, thereby constituting anaberration correcting system for correcting an aberration distortion dueto an orthogonal shift and the like of a beam spot projected onto arecording surface of the disk to obtain a preferable reproduction signalwaveform.

FIG. 11 shows a construction of an optical pickup 2′ in the optical diskapparatus of the second embodiment, where 2 a denotes an object lens and2 h denotes a liquid crystal aberration correction unit adapted to theaberration correcting system.

FIG. 12 shows a constitution example of the liquid crystal (LC)correction unit 2 h where the liquid crystal correction unit 2 h isdivided into, for example, four segments in the track tangentialdirection of the disk, that is, first to fourth LC tilt correctionelements 2 i, 2 j, 2 k and 2 m arranged in this order in the diskrotational direction. Each segment of the tilt correction elements iscomposed of a liquid crystal element having a variable light refractiveindex independently.

Next, the following describes the operation of the second embodimenthaving the construction mentioned above in connection with only thedifferent portions from the first embodiment, and explanation of theredundant portions is omitted here. In this operation, it can be assumedthat the aberration in the track tangential direction of the disk ismainly caused by a T tilt. Therefore, the method of detecting theorthogonal shift described in the first embodiment can be employed inthis embodiment, using a comparison in the combination of the tapcoefficients obtained by the adaptive equalizer 8.

Thus, in the aberration detector 13, in a similar manner to that of theorthogonal shift detection, the aberration detection signal can beobtained using the comparison in each pair of the tap coefficientsobtained by the FIR filter portion 21 of the adaptive equalizer 8. Forexample, assuming that the light refractive indexes of the first throughfourth tilt correction elements 2 i, 2 j, 2 k and 2 m are n1, n2, n3 andn4 in this order, when (C7−C1) is plus, the aberration controller 14appropriately controls each of the refractive indexes to be n1<n2<n3<n4.When (C7−C1) is minus, the aberration controller 14 controls each of therefractive indexes to be n1>n2>n3>n4 so that the aberration can becorrected.

As described above, according to the second embodiment of the presentinvention, the aberration control adaptive to each position of the diskcircumferential direction can be effectively executed for the disk ordrive system including the optical pickup having an aberration in thetrack tangential direction of the disk. Therefore, the most preferablereproduction signal can be produced in the disk reproducing apparatus,and a good reproduction margin can be secured even when using a diskwith high recoding density.

It is noted here that, although the liquid crystal aberration correctingunit 2 h is divided into four segments, it is not limited to this anddivision and type thereof can be appropriately changed according to thetype of the aberration to be corrected. For example, as shown in FIG.13, a liquid crystal aberration correcting unit 2 h′ may be divided intothree segments, that is, first to third tilt correction elements 2 i, 2j and 2 k, where the first and third elements 2 i and 2 k respectivelyhaving refractive indexes n1 and n3 are arranged in the track tangentialdirection of the disk rotational direction and the second element 2 joccupies the radial center portion and surrounding portion thereof.Moreover, the optical pickup 2′ having the liquid crystal aberrationcorrecting unit 2 h or 2 h′ of the second embodiment may be used incombination with the tilt controlling apparatus having the orthogonalshift detector 9 and tilt controller 10 of the first embodiment.

Third Embodiment

FIG. 14 shows a block construction of an optical disk apparatusaccording to the third embodiment of the present invention. In thisembodiment, the tilt control system of the first embodiment as shown inFIG. 1 is employed, and a different point therefrom is that a systemcontroller (control CPU) 15 is further provided for controlling theadaptive equalizer 8, orthogonal shift detector 9, tilt controller 10and optical pickup device 2 to consntitute a data recording andreproducing apparatus. It is noted here that FIG. 14 mainly shows theconstruction of the disk reproducing system, omitting the constructionof the disk recording system here since the disk recording system isalready described with reference to FIG. 19.

FIGS. 15A through 15G show timing charts in connection with a sectorformat of a recording guide groove formed on e.g. a DVD-RAM as a diskmedium, where FIG. 15A shows a disk sector format, each sector iscomprised of a prepit address region 61 formed of emboss prepits and aninformation (i.e., user data) recording region 62 having, for example, aperiodically wobbling recording guide groove. The prepit address region61 is shifted by a half track distance from the recording guide groove.The information recording region 62 is a data rewritable region forrecording user data. FIGS. 15B and 15C show the RF signals output of thepreamplifier 3 when recording of the user data information is notexecuted (FIG. 15B) and when recording of the user data information isexecuted (FIG. 15C). FIGS. 15D through 15G show various control signalssuch as a prepit address gate signal PAG, recording gate signal RG,reproduction gate signal RPG and learning reproduction gate signal LRPG,respectively, which the control gate signals are generated by the systemcontroller 15.

The following describes the control operation of the optical diskapparatus according to the third embodiment with reference to FIGS. 14and 15, concentrating attention to the difference point from the firstembodiment.

In the recording operation for recording data to the optical disk, whenthe optical pickup seeks and tracks a sector to be recorded, the systemcontroller 15 transmits the prepit address gate signal PAG to theadaptive equalizer 8, orthogonal shift detector 9 and tilt controller10. When the prepit address gate signal PAG is in High (=1) level, theadaptive equalizer 8 executes the adaptive equalization so that thereproduction signal read out of the prepit address region 61 is madeoptimal, and the orthogonal shift detector 9 calculates a tapcoefficient comparison of, for example, (C7−C1) upon receipt of the tapcoefficients of the FIR filter 21 and generates the orthogonal shiftsignal. The tilt controller 10 controls the tilt actuator of the opticalpickup 2 in the same manner as that of the tilt control operationdescribed in the first embodiment. Thus, the orthogonal shift betweenthe disk surface and the optical axis of the light beams of the opticalpickup is made minimum (i.e, substantially zero).

When the optical pickup 2 advances to track the information recordingregion 62 and the prepit address gate signal PAG is in Low (=0) level,the system controller 15 transmits the recording gate signal RG to theoptical pickup 2 while the last control operations to the prepit addressregion 61 executed by the adaptive equalizer 8, orthogonal detector 9and tilt controller 10 are maintained in this region. Upon receipt ofthe recording gate signal RG, the optical pickup 2 is controlled by thelaser drive unit (LPC) shown in FIG. 19 to record the desired user datasignal to the disk during the High (=1) level of the recording gatesignal RG.

Next, in the reading operation for reproducing data from the opticaldisk, in a similar manner to that of the recording operation, when theprepit address gate signal PAG is in High (=1) level, the adaptiveequalizer 8 executes the adaptive equalization so that the reproductionsignal read out of the prepit address region 61 is made optimal, and theorthogonal shift detector 9 calculates, for example, (C7−C1) uponreceipt of the tap coefficients of the FIR filter 21 and generates theorthogonal shift signal. The tilt controller 10 controls the tiltactuator of the optical pickup 2, so that the orthogonal shift betweenthe disk surface and the optical axis of the light beams of the opticalpickup is made minimum (i.e, substantially zero).

When the optical pickup 2 advances to track the information recordingregion 62 and the prepit address gate signal PAG is in Low (=0) level,the system controller 15 transmits the reproduction gate signal RPG tothe adaptive equalizer 8 while the last control operations to the prepitaddress region 61 executed by the orthogonal detector 9 and tiltcontroller 10 are maintained. Subsequently, the reproduction signal ofthe data information read out of the information recording region 62 issupplied to the adaptive equalizer 8 via the preamplifier 3, AGC 4,equalizer 5 and via the A/D converter 6. As the reproduction signals ofthe prepit address region 61 and the information recording region 62 aredifferent in signal quality, the adaptive equalizer 8 newly executes theadaptive equalization to the information recording region 62 so that thedisk reproduction signal is made into the optimal reproduction signal,and the error due to inter-code interference remaining after conductingthe tilt control is processed to be eliminated. Then the resultantoptimal reproduction signal is applied to the Viterbi decoder 11. TheViterbi decoder 11 digitizes the input reproduction signal and thebinary NRZI signal is demodulated by the demodulator 12 and theresultant reproduction data of the recovered user data format is sentout to a subsequent processing unit (not shown).

As described above, according to the third embodiment, even in therecording operation for recording data to the optical disk, an adaptivetilt control can be executed in each position of the track tangentialdirection of the disk to the disk or disk drive system having a T tilt.Accordingly, when the data is recorded to the disk, the recordingoperation can be performed in the optimally T tilt controlled condition.Also, in the data reproducing operation, the reproduction signal can beformed in the optimally T tilt controlled condition. Thus, a goodrecording and reproducing margin can be obtained in the disk even havinga high recording density.

It is noted here that, although the adaptive equalization and tiltcontrol are executed over the enntire part of the prepit address region61 in the third embodiment, these control operations can be executedusing a part of the prepit address region. Moreover, although therecording operation is conducted at the same time of equalizationlearning control operation of the reproduction signal read our of theprepit address region, it may be possible that the learned result of theorthogonal shift signal is previously stored in a temporary storageportion and the stored orthogonal shift signal is used to conduct thetilt control when the data is recorded to the disk. Moreover, the trackto be previously learned may be different from a target track to berecorded.

In addition, in the third embodiment, although the tilt control in thedata reproducing operation is executed only based on the reproduciotndata of the prepit address region 61 and the tilt control is maintainedin the reproducing operation of the user data information of theinformation recording region 62, the tilt control may be always executedalso in the reproducing operation of the user data information of theinformation recording region 62 in a similar manner to that of the firstembodiment.

Fourth Embodiment

FIG. 16 shows a block construction of an optical disk apparatusaccording to the fourth embodiment of the present invention. In thisembodiment, the aberration correction control system of the secondembodiment as shown in FIG. 10 is employed, and a different pointtherefrom is that a system controller (control CPU) 15 is furtherprovided for controlling the adaptive equalizer 8, aberration detector13, aberration controller 14 and optical pickup device 2 to consntitutea data recording and reproducing apparatus. It is noted here that FIG.16 mainly shows the construction of the disk reproducing system,omitting the construction of the disk recording system here since thedisk recording system is already described with reference to FIG. 19.Therefore, the difference point from the third embodiment is that, theoptical pickup 2 is replaced by the optical pickup 2′, the orthogonalshift detector 9 is replaced by the aberration detector 13 and the tiltcontroller 10 is replaced by the aberration controller 14.

The following describes the control operation of the optical diskapparatus according to the fouth embodiment with reference to FIGS. 15and 16, concentrating attention to the difference point from the secondembodiment.

In the recording operation for recording data to the optical disk, whenthe optical pickup seeks and tracks a sector to be recorded, the systemcontroller 15 transmits the prepit adress gate signal PAG to theadaptive equalizer 8, aberration detector 13 and aberration controller14. When the prepit address gate signal PAG is in High (=1) level, theadaptive equalizer 8 executes the adaptive equalization so that thereproduction signal read out of the prepit address region 61 is madeoptimal, and the aberration detector 13 calculates a tap coefficientcomparison of, for example, (C7−C1) upon receipt of the tap coefficientsof the FIR filter 21 and generates the aberration detection signal. Theaberration controller 14 controls the liquid crystal tilt correctionunit 2 h of the optical pickup 2′ to adjust the light refractive indexesof the first to fourth liquid crystal tilt correction elements 2 i, 2 j,2 k and 2 m, indivisually in the same manner as that of the aberrationcorrection control operation described in the second embodiment. Thus,the aberration of the light is beams is made minimum (i.e, substantiallyzero).

When the optical pickup 2′ advances to track the information recordingregion 62 and the prepit address gate signal PAG is in Low (=0) level,the system controller 15 transmits the recording gate signal RG to theoptical pickup 2′ while the last control operations to the prepitaddress region 61 executed by the adaptive equalizer 8, aberrationdetector 13 and aberration controller 14 are maintained in this region.Upon receipt of the recording gate signal RG, the optical pickup 2′ iscontrolled by the laser drive unit (LPC) shown in FIG. 19 to record thedesired user data signal to the disk during the High (=1) level of therecording gate signal RG.

Next, in the reading operation for reproducing data from the opticaldisk, in a similar manner to that of the recording operation, when theprepit address gate signal PAG is in High (=1) level, the adaptiveequalizer 8 executes the adaptive equalization so that the reproductionsignal read out of the prepit address region 61 is made optimal, and theaberration detector 13 calculates, for example, (C7−C1) upon receipt ofthe tap coefficients of the FIR filter 21 and generates the aberrationdetection signal. The aberration controller 14 controls the liquidcrystal tilt correction unit 2 h of the optical pickup 2′ toindividually adjust the first to fourth tilt correction elements 2 i, 2j 2 k and 2 m, so that the aberration is made minimum (i.e,substantially zero).

When the optical pickup 21 advances to track the information recordingregion 62 and the prepit address gate signal PAG is in Low (=0) level,the system controller 15 transmits the reproduction gate signal RPG tothe adaptive equalizer 8 while the last control operations to the prepitaddress region 61 executed by the aberration detector 13 and aberrationcontroller 14 are maintained. Subsequently, the reproduction signal ofthe data information read out of the information recording region 62 issupplied to the adaptive equalizer 8 via the preamplifier 3, AGC 4,equalizer 5 and via the A/D converter 6. As the reproduction signals ofthe prepit address region 61 and the information recording region 62 aredifferent from each other in signal quality, the adaptive equalizer 8newly executes the adaptive equalization to the information recordingregion 62 so that the disk reproduction signal is made into the optimalreproduction signal, and the error due to inter-code interferenceremaining after conducting the aberration correction control isprocessed to be eliminated. Then the resultant optimal reproductionsignal is applied to the Viterbi decoder 11. The Viterbi decoder 11digitizes the input reproduction signal and the binary NRZI signal isdemodulated by the demodulator 12 and the is resultant reproduction dataof the recovered user data format is sent out to a subsequent processingunit (not shown).

As described above, according to the fourth embodiment, even in therecording operation for recording data to the optical disk, an adaptiveaberration correction control can be executed in each position of thetrack tangential direction of the disk to the disk or disk drive systemhaving an aberration in the track tangential direction. Accordingly,when the data is recorded to the disk, the recording operation can beperformed in the optimally aberration correction controlled condition.Also, in the data reproducing operation, the reproduction signal can beformed in the optimally aberration correction controlled condition.Thus, a good recording and reproducing margin can be obtained evenhaving a high recording density in the disk.

It is noted here that, in the fourth embodiment, although the adaptiveequalization and aberration correction controls are executed over theenntire part of the prepit address region 61, these control operationscan be executed using a part of the prepit address region. Moreover,although the recording operation is conducted at the same time of theequalization learning control operation in the data reproducingoperation reading our of the prepit address region, it may be possiblethat the learned result of the aberration detection signal is previouslystored in a temporary storage portion and the stored aberrationdetection signal is used to conduct the aberration correction controlwhen the data is recorded to the disk. Moreover, the track to bepreviously learned may be different from a target track to be recorded.

In addition, in the fourth embodiment, although the aberrationcorrection control in the data reproducing operation is executed onlybased on the reproduciotn data of the prepit address region 61 and theaberration correction control is maintained in the reproducing operationof the user data information of the information recording region 62, theaberration correction control may be always executed also in the datareproducing operation of the user data information of the informationrecording region 62 in a similar manner to that of the secoxndembodiment.

Fifth Embodiment

FIG. 17 shows a block construction of an optical disk apparatusaccording to the fifth embodiment of the present invention which isbasically similar to that of the third embodiment shown in FIG. 14. Inthis fifth embodiment, the difference poin from the third embodiment ismerely that the kind of the control gate signals output of the systemcontroller 15 and the connecting destination thereof are changed fromthose of the third embodiment.

The following describes the control operation of the optical diskapparatus according to the fifth embodiment with reference to FIGS. 15and 17, concentrating attention to the difference point from the thirdembodiment.

When the disk apparatus is started or immediately before the recordingoperation, the tracking controller controls the optical pickup to seek atrack for learning the tilt control provided on the optical disk. Then,the tilt control is fixed to a neutral position and the learninginformation is recorded to the information recording region 62 duringthe High level 1 of the recording gate signal RG generated by the systemcontroller 15. Next, the information recorded on the subject track forlearning is reproduced while the tilt control remins to be fixed to theneutral condition, and the informationto recorded to the informationrecording region 62 is reproduced during the High level 1 of thelearning reproduction gate signal LRPG shown in FIG. 15G. Upon receiptof the learning reproduction gate signal LRPG, the adaptive equalizer 8executes the adaptive equalization so that the reproduction signal readout of the information recording region 62 is made optimal, and theorthogonal shift detector 9 calculates a tap coefficient comparison of,for example, (C7−C1) of the tap coefficients of the FIR filter 21 andgenerates the orthogonal shift signal. The tilt controller 10 previouslyand temporarily stores the orthogonal shift signal for an informationamount of one track in a temporary storage portion 10 a in associationwith the position in the track tangential direction of the disk.

When the optical pickup 2 advances to track a sector to be recorded, thesystem controller 15 transmits the recording gate signal RG to theoptical pickup 2 and to the tilt controller 10. During the High level 1of the recording gate signal RG, the tilt controller 10 controls thetilt actuator of the optical pickup 2 in accordance with the orthogonalshift signal previously stored in the temporary storage portion 10 a sothat the orthogonal shift is made minimum. Upon receipt of the recordinggate signal RG, the optical pickup 2 is controlled by the laser driveunit (LPC) shown in FIG. 19 to record the desired data signal to thedisk during the High (=1) level of the recording gate signal RG.

Next, in the reading operation for reproducing data from the opticaldisk, in a similar manner to that of the recording operation, when theoptical pickup 2 advances to track a sector to be reproduced, the systemcontroller 15 transmits the reproduction gate signal RPG to the adaptiveequalizer 8 in common to the tilt controller 10. During the High level 1of the reproduction gate signal RPG, the tilt controller 10 controls thetilt actuator of the optical pickup 2 in accordance with the orthogonalshift signal previously stored in the temporary storage portion 10 a sothat the orthogonal shift is made minimum. Subsequently, thereproduction signal of the data information read out of the informationrecording region 62 is supplied to the adaptive equalizer 8 via thepreamplifier 3, AGC 4, equalizer 5 and via the A/D converter 6. Theadaptive equalizer 8 renews the tap coefficients and newly executes theadaptive equalization to the information recording region 62 so that thedisk reproduction signal is made into the optimal reproduction signal,and the error due to inter-code interference remaining after conductingthe tilt control is processed to be eliminated. Then the resultantoptimal reproduction signal is applied to the Viterbi decoder 11. TheViterbi decoder 11 digitizes the input reproduction signal and thebinary NRZI signal is demodulated by the demodulator 12 and theresultant reproduction data of the recovered user data format is sentout to a subsequent processing unit (not shown).

As described above, according to the fifth embodiment, even in therecording operation for recording data to the optical disk, an adaptivetilt control can be executed in each position of the disk tracktangential direction to the disk or disk drive system having a T tilt.Accordingly, when the data is recorded to the disk, the recordingoperation can be performed in the control condition optimally regulatingthe T tilt. Also, in the data reproducing operation, the reproductionsignal can be formed in the control condition optimally regulating the Ttilt. Thus, a good recording and reproducing margin can be obtained inthe disk even having a high recording density.

It is noted here that, as a recording track for preciously learning, aneighboring track adjacent to the subject track to be recorded may beused. Moreover, the recording track for preciously learning may be asubject track per se before subject to overwrite. The recording trackfor preciously learning may be a track adjacent to the subject track tobe recorded where the track for learning has recorded the learninginformation immediately before the adjacent recording track is subjectto recording.

In addition, in the fifth embodiment, although the adaptive equalizationlearning is executed only during the High level 1 of the learningreproduction gate signal LRPG and the tilt control in recording orreproducing operation is executed only during the High level 1 of therecording gate signal RG or reproduction gate signal RPG, the adaptiveequalization learning may be executed together with the prepit addressregion 61 and the tilt control in recording or reproducing operation maybe executed conticuously over the information recording region 62together with the prepit address region 61.

In addition, in the fifth embodiment, although the control operation isdescribed with reference to the optical disk apparatus using arewritable optical disk, i.e., RAM disk for both read and write, theleraning information may be recorded on a track for learning, readingonly or any optional track in a reproducing operation of a ROM disk andthe tilt control may be executed using the learning information recordedon the track when a target track to be read is reproduced. Moreover, thelearning information result may be a control signal for tilt-controllingthe actuator in accordance with the orthogonal shift signal.

Sixth Embodiment

FIG. 18 shows a block construction of an optical disk apparatusaccording to the sixth embodiment of the present invention which isbasically similar to that of the fourth embodiment shown in FIG. 16. Inthis sixth embodiment, the difference poin from the fourth embodiment ismerely that the kind of the control gate signals output of the systemcontroller 15 and the connecting destination thereof are changed fromthose of the fourth embodiment.

The following describes the control operation of the optical diskapparatus according to the sixth embodiment with reference to FIGS. 15and 18, concentrating attention to the difference point from the fourthembodiment.

When the disk apparatus is started or immediately before the recordingoperation, the tracking controller controls the optical pickup to seek atrack for learning the aberration control information on the opticaldisk. Then, the aberration control is fixed to a neutral position andthe learning information is recorded to the information recording region62 during the High level 1 of the recording gate signal RG. Next, theinformation recorded on the subject track for learning is reproducedwhile the aberration control remins to be fixed to the neutralcondition, and the informationto recorded to the information recordingregion 62 is reproduced during the High level 1 of the learningreproduction gate signal LRPG shown in FIG. 15G. Upon receipt of thelearning reproduction gate signal LRPG, the adaptive equalizer 8executes the adaptive equalization so that the reproduction signal readout of the information recording region 62 is made optimal, and theaberration detector 13 calculates a tap coefficient comparison of, forexample, (C7−C1) of the tap coefficients of the FIR filter 21 andgenerates the aberration detection signal. The aberration controller 14previously and temporarily stores the aberration detection signal for aninformation amount of one track in a temporary storage portion 14 a inassociation with the position in the track tangential direction of thedisk.

When the optical pickup 2′ advances to track a sector to be recorded,the system controller 15 transmits the recording gate signal RG to theoptical pickup 2′ and in common to the aberration controller 14. Duringthe High level 1 of the recording gate signal RG, the aberrationcontroller 14 controls the liquid crystal tilt correction unit 2 h ofthe optical pickup 2′ in accordance with the aberration detection signalpreviously stored in the temporary storage portion 14 a so that theaberration is made minimum by individually adjusting the lightrefractive indexes of the first through fourth segments of the tiltcorrection elements 2 i, 2 j, 2 k and 2 m. Upon receipt of the recordinggate signal RG, the optical pickup 2′ is controlled by the laser driveunit (LPC) shown in FIG. 19 to record the desired data signal to thedisk during the High (=1) level of the recording gate signal RG.

Next, in the reading operation for reproducing data from the opticaldisk, when the optical pickup 2′ advances to track a sector to bereproduced, the system controller 15 transmits the reproduction gatesignal RPG to the adaptive equalizer 8 in common to the aberrationcontroller 14. During the High level 1 of the reproduction gate signalRPG, the aberration controller 14 controls the liquid crystal tiltcorrection unit 2 h of the optical pickup 2′ in accordance with theaberration detection signal previously stored in the temporary storageportion 14 a so that the aberration is made minimum by individuallyadjusting the light refractive indexes of the first through fourthsegments of the tilt correction elements 2 i, 2 j, 2 k and 2 m.

Subsequently, the reproduction signal of the data information read outof the information recording region 62 is supplied to the adaptiveequalizer 8 via the preamplifier 3, AGC 4, equalizer 5 and via the A/Dconverter 6. The adaptive equalizer 8 renews the tap coefficients andexecutes the adaptive equalization to the information recording region62 so that the disk reproduction signal is made into the optimalreproduction signal, and the error due to inter-code interferenceremaining after conducting the aberration corection control is processedto be eliminated. Then the resultant optimal reproduction signal isapplied to the Viterbi decoder 11. The Viterbi decoder 11 digitizes theinput reproduction signal and the binary NRZI signal is demodulated bythe demodulator 12 and the resultant reproduction data of the recovereduser data format is sent out to a subsequent processing unit (notshown).

As described above, according to the sixth embodiment, even in therecording operation for recording data to the optical disk, an adaptiveaberration correction control can be executed in each position of thedisk track tangential direction to the disk or disk drive system havingan aberration in a track tangential direction. Accordingly, when thedata is recorded to the disk, the recording operation can be performedin the control condition optimally regulating the aberration. Also, inthe data reproducing operation, the reproduction signal can be formed inthe control condition optimally regulating the aberration. Thus, a goodrecording and reproducing margin can be obtained in the disk having ahigh recording density.

It is noted here that, as a recording track for preciously learning, aneighboring track adjacent to the subject track to be recorded may beused. Moreover, the recording track for preciously learning may be asubject track per se before subject to overwrite. The recording trackfor preciously learning may be a track for learning previously subjectedto recording. The recording track for preciously learning may be a trackadjacent to the subject track to be recorded where the track forlearning has recorded the learning information immediately before theadjacent recording track is subject to recording.

In addition, in the sixth embodiment, although the adaptive equalizationlearning is executed only during the High level 1 of the learningreproduction gate signal LRPG and the aberration control in recording orreproducing operation is executed only during the High level 1 of therecording gate signal RG or reproduction gate signal RPG, the adaptiveequalization learning may be executed together with the prepit addressregion 61 and the aberration control in recording or reproducingoperation may be executed conticuously over the information recordingregion 62 together with the prepit address region 61.

In addition, in the sixth embodiment, although the control operation isdescribed with reference to the optical disk apparatus using arewritable optical disk, i.e., RAM disk for both read and write, theleraning information may be recorded on a track for learning, readingonly or any optional track in a reproducing operation of a ROM disk andthe aberration control may be executed using the learning informationrecorded on the track when a target track to be read is reproduced.

As described above, according to the first aspect of the presentinvention, even in the case where an optical disk or a drive systemhaving an optical pickup includes a T tilt, an optimal tilt control canbe executed adaptively in each position of the track tangentialdirection of the disk with high accuracy and a simple construction.Thus, the optimal reproduction signal can be produced in the diskreproducing system, and the disk reproduction margin can be secured evenwith a high recording density of the disk.

According to the second aspect of the present invention, the aberrationcontrol adaptive to each position of the disk circumferential directioncan be effectively executed for the disk or drive system including theoptical pickup having an aberration in the track tangential direction ofthe disk. Therefore, the optimal reproduction signal can be produced inthe disk reproducing apparatus, and a good reproduction margin can besecured even using a disk with high recoding density.

According to the third aspect of the present invention, even in therecording operation for recording data to the optical disk, an adaptivetilt control can be executed in each position of the disk tracktangential direction to the disk or disk drive system having a T tilt.Accordingly, when the data is recorded to the disk, the recordingoperation can be performed in the optimally T tilt controlled condition.Also, in the data reproducing operation, the reproduction signal can bemade optimal. Thus, a good recording and reproducing margin can beobtained in the disk even having a high recording density. Moreover, thecontrol learning operation is executed on the recording track, and ahigh accuracy of the tilt control can be obtained.

According to the fourth aspect of the present invention, even in therecording operation for recording data to the optical disk, an adaptiveaberration control can be executed in each position of the disk tracktangential direction to the disk or disk drive system having anaberration in a disk track tangential direction. Accordingly, when thedata is recorded to the disk, the recording operation can be performedin the condition optimally correcting the aberration. Also, in the datareproducing operation, the reproduction signal can be made optimal.Thus, a good recording and reproducing margin can be obtained in thedisk having a high recording density. Moreover, the control learningoperation is executed on the recording track, and a high accuracy of theaberration control can be obtained.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Such changes and modificationsare to be understood as included within the scope of the presentinvention as defined by the appended claims, unless they departtherefrom.

1. An optical disk apparatus for recording and reproducing informationto and from an optical disk, the optical disk apparatus comprising: anoptical pickup for irradiating a light beam onto an optical disk surfacefor recording and reproducing the information to generate an analogreproduction signal therefrom; an A/D converter for converting theanalog reproduction signal into a digital reproduction signal anadaptive equalizer for receiving the digital reproduction signal fromthe A/D converter and adaptively renewing a plurality of tapcoefficients of a FIR filter; and an aberration control apparatus forminimizing an aberration contained in a spot of a light beam irradiatedfrom the optical pickup onto the optical disk, wherein the aberrationcontrol apparatus comprises: an aberration detector for detecting theaberration of the light beam spot using the tap coefficients of theadaptive equalizer and generating an aberration detection signal inaccordance with the detected aberration; an aberration correcting unitfor correcting the aberration of the light beam spot; and a correctioncontrol unit for controlling the aberration correction of the aberrationcorrecting unit in accordance with the aberration detection signal tominimize the aberration of the light beam spot, wherein the aberrationdetector is operable to detect the aberration by comparing at least onepair of the tap coefficients that are symmetrical with respect to acenter position in time delay order thereof, and wherein a number of theplurality of the tap coefficients is odd, and the correction controlunit is operable to control the aberration correction of the aberrationcorrecting unit in a manner that at least a symmetrical pair of the tapcoefficients are made substantially coincident with each other.